Structural, electronic properties and heat of formation of Mg2FeH6 complex hydride: an ab initio study

In this work, the structural, energetic and electronic properties of Mg2FeH6 complex hydride have been studied using two different methods based on the density functional theory (DFT): the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and the pseudo-potentials plane waves (PP-PW) methods. Based on the calculated results, the ground state of Mg2FeH6 is found to be paramagnetic (PM), which is in agreement with experimental results, and also, the optimized structural parameters including lattice constants and atomic positions are very close to the experimental and other theoretical works. For a detailed study, electronic structure calculations including those of the energy band, density of states (DOS) and charge density distribution have been performed. It is found that Mg2FeH6 hydride is a semiconductor with a direct energy gap at the X-point of about 1.87 and 2.25 eV for the FP-LAPW + lo and PW-PP methods, respectively, and the Mg atom acts as a donor to form a cation ion and the negatively charged FeH6 complex results in a mainly ionic bonding between the Mg and FeH6 complex. Other physical and energetic properties such as bulk modulus, cohesive energy and formation enthalpy of Mg2FeH6 are in good agreement with the theoretically and experimentally determined values. (paper)